1. Field of the Invention
The present invention relates to a disc cartridge in which a disc-like recording medium such as an optical disc, a photomagnetic disc and a magnetic disc is accommodated rotatably in a disc-accommodating chamber of a cartridge case. More specifically, the present invention relates to a disc cartridge in which by rotating an intermediate shell for forming a disc accommodating chamber with an upper shell or a lower shell, a pair of shutter members are opened/closed so as to open/close an opening portion and when it is opened, part of the disc-like recording medium is exposed through the opening portion.
2. Description of the Related Art
Conventionally, as a disc cartridge in which a disc-like recording medium allowing recording/reproduction of information such as audio, video and computer data is accommodated rotatably in a cartridge case thereof, a disc cartridge having a structure shown in FIG. 42 has been well known. This disc cartridge 1 contains an additionally writable photomagnetic disc 4 allowing information such as computer data to be additionally written therein and has an external shape shown in FIG. 42.
This disc cartridge 1 comprises a cartridge case 2 composed of a pair of an upper shell 2a and a lower shell 2b, a photomagnetic disc 4 accommodated rotatably in the disc accommodating chamber 3 of the cartridge case 2 and the like. A top face and a bottom face of the cartridge case 2 have upper and lower opening portions 5 extending from the center portion to a side thereof. The opening portions 5 can be opened/closed by a shutter member 6 capable of sliding along a side. This shutter member 6 is always urged in a direction of closing the opening portion 5 by a spring (not shown). Reference numeral 6a denotes a pressing member for preventing a front end of the shutter member 6 from slipping out.
A center hub 7 formed of metal in a circular shape is provided in the center of the photomagnetic disc 4. This center hub 7 is disposed at a position corresponding to an inside end of the opening portion 5, that is, substantially in the center of the cartridge case 2. A turntable provided on the main body of an information recording/reproducing apparatus is loaded on this center hub 7. Then, the center hub 7 is chucked by the turntable, so that the photomagnetic disc 4 is driven at a predetermined speed (for example, constant linear speed). By means of a photomagnetic pickup unit whose head portion is inserted into the opening portion 5, recording and reproduction of information signal from/into the photomagnetic disc 4 are carried out.
In the conventional disc cartridge having such a structure, the shutter member 6 for opening/closing the opening portion 5 is formed to have a U-shaped section and this shutter member 6 is fit to a side of the cartridge case 2 such that the shutter member 6 is slidable along that side to open/close the opening portion 5. Thus, because a large gap is generated between the cartridge case 2 and the shutter member 6, it is difficult to block invasion of minute dirt, dust and the like.
In the recent trend of increased capacity of the optical disc and intensified recording density, narrowed pitches in recording patterns and an increase in line density have been accelerated. If dust or dirt invades onto a recording face of the optical disc or photomagnetic disc, reading or writing beam may be intercepted or normal reading/writing of information may be disabled by damage on the information recording face. Thus, in the conventional disc cartridge, as shown in FIG. 42, the shutter member 6 formed to have the substantially U-shaped section is mounted slidably on a side of the cartridge case 2 and by moving the shutter member 6 along the side, the opening portion is opened/closed so as to protect information recording face of the optical disc or the like.
Because of the trend of further increased capacity and intensified recording density, minute dust and dirt, which hardly affect conventionally, influence reading and writing of data more seriously. However, the shutter member formed to have the above-described substantially U-shaped section is incapable of blocking the infiltration of such minute dust and dirt. If the minute dust or dirt infiltrating into the cartridge case 2 is attached to the information recording face of the photomagnetic disc 4, the information recording face is damaged by this dirt or dust, so that proper reading and writing of information are disabled.
Further, because in the conventional disc cartridge 1, the shutter member 6 is located at a position where a user is likely to touch, he may slide the shutter member 6 by mistake to open the opening portion 5. Further, because the shutter member 6 is always urged in the direction of closing the opening portion 5 by a spring (not shown), not only the spring is needed as a component, but also it takes much labor and time to assemble the spring, thereby leading to poor assembly efficiency and productivity of such a disc cartridge.